1. Field of the Invention
This invention relates to down-hole drilling motors, such as turbodrills and drills operated by positive displacement motors, and more particularly to improved bearings used therein.
2. Brief Description of the Prior Art
Down-hole drilling motors were first invented 100 years ago. Down-hole drilling motors were first extensively tested in the 1920's. They did not find wide spread use until the 1950's when turbodrills began to be used in the Soviet Union. By the early 1960's, it is estimated that 85% of the wells in the Soviet Union were being drilled with turbodrills. Down-hole drilling motors have found widespread use in the United States for drilling directional holes, but they are not widely used for straight hole drilling because of bearing and seal problems.
Commerical down-hole drilling motors operate most effectively at speeds of 50 to 150 rpm. At high motor speeds, roller bearings fail after periods of about 5 to 15 hours whereas with conventional drilling equipment operating at lower speeds the bearings of roller bit last up to 200 hours. Down-hole motors have had substantial problems in design of radial and vertical thrust bearings, lubrication systems, turbine efficiency, housing construction, etc., which have limited substantially the acceptability of down-hole motros in petroleum drilling and in other applications.
Down-hole drilling motors were patented soon after the element of rotary drilling rigs in the 1860's.
Cross U.S. Pat. No. 174,922 discloses a very primitive turbodrill.
Baker U.S. Pat. No. 292,888 dicloses a single stage axial flow turbodrill which is similar in some respects to modern turbodrills.
Scharpenberg U.S. Pat. No. 2,482,702 discloses one of the earliest multi-stage turbodrills which was the forerunner of turbodrills currently in use. The Scharpenberg turbodrill contained a lubrication system which allowed the thrust bearing to operate in oil or grease. Drilling fluid acting on a floating piston pressurized the lubricant in the system. The bearing in modern turbodrills operate directly in the abrasive driling mud, resulting in rapid failures, which limit the application of these drills.
Capeliuschnicoff U.S. Pat. No. 1,681,094 dicloses a single staged geared turbodrill. These turbodrills were tested extensively in the Soviet Union from 1924 to 1934. The Russians had severe problems with the speed reducers Capeliuschnicoff turbodrill and subsequently changed to the Scharpenberg turbodrill. Several Russian engineers perfected multi-stage turbodrills during the 1940's and 1950's and by the early 1960's, the Russians were drilling 80 to 90% of their wells with axial flow turbodrills. The Russians licensed turbodrill technology to companies in the United States, France, Germany and Austria. Turbodrills have had a rather limited commerical acceptance and are used primarily in directional wells.
Virtually all down-hole drilling motors have four basic components;
1. Motor section PA1 2. Vertical thrust bearings PA1 3. Radial bearings PA1 4. Rotary seal. PA1 1. Turbodrills PA1 2. Positive displacement PA1 1. Moineau motors PA1 2. Flexing vane motors PA1 3. Sliding vane motors PA1 1. Rubber friction bearings PA1 2. Ball or roller bearings PA1 1. Marine bearings PA1 2. Roller or ball bearings PA1 1. Packing seals PA1 2. Face seals PA1 3. Labyrinth seals PA1 4. Radial lip seals PA1 5. Constrictions (friction bearings and marine bearings) PA1 6. Flow metering seals
The bearings and seals can be placed in a separate package or unit at the motor section and thus can be used on any type of motor (i.e. turbodrills, positive displacement motors, etc.)
There are two basic types of down-hole drilling motors:
Turbodrills utilize the momentum change of drilling fluid (i.e. mud) passing through the curved turbine blades to provide torque to turn the bit. Diamond bits are used on most turbodrills because these motor turn at speed of 600 to 1,000 rpm whereas roller-type rock bits operate effectively only at speeds up to about 150 rpm. Positive displacement motors have fixed volumetric displacement and their speed is directly proportional to the flow rate. There are three basic types of positive displacement motors in use or currently under development:
These motors have large volumetric displacement and therefor deliver higher torques at lower speeds.
Thrust bearing failure in down-hole motors is a problem because of high dynamic leads produced by the action of the bits and by drill string vibrations. One major oil company placed a recorder at the hole bottom and found that dynamic loads were often 50% higher than the applied bit weight. It was found on occasion that the bit bounced off bottom and produced loads in excess of 120,000 pounds when drilling at an applied bit weight of 40,000 pounds. These high loads can cause rapid failure of the thrust bearings; consequently these bearings must be greatly over designed to operate in the hostile down-hole environment.
Two types of bearing have been used in down-hole drilling motors:
In existing motors, these bearings operate directly in the abrasive drilling mud and usually wear out in 20 to 100 hours. In addition, the rubber friction bearings have high friction and therefore absore 30 to 40% of the output torque of the turbodrills. The lift of the vertical thrust bearings can be increased by operating at bit weights which nearly balance the hydraulic down thrust thereby removing most of the load from these bearings.
Radial bearings are required on each side of drilling motors and on each side of the vertical thrust bearings. These radial bearings are usually subjected to lower loads than the thrust bearings and therefore have much longer life. Two basic types of radial bearings are used in down-hole motors:
Most motors contain marine bearings made of brass, rubber or similar bearing materials. The marine bearings are cooled by circulated mud through them.
In the commonly assigned U.S. Pat. Nos. 4,114,702; 4,114,703 and 4,114,704 an improved turbodrill is disclosed which utilizes roller bearings both for radial bearings and longitudinal thrust bearings.
It is well known to use diamond bits for earth drilling using natural or synthetic diamonds bonded to supporting metallic or carbide studs or slugs. There are several types of diamond bits known to the drilling industry. In one type, the diamonds are a very small size and randomly distributed in a supporting matrix. Another type contains diamonds of a larger size positioned on the surface of a drill shank in a predetermined pattern. Still another type involves the use of a cutter formed of a polycrystalline diamond supported on a sintered carbide support.
Some of the most recent publications dealing with diamond bits of advanced design are Rowley, et al. U.S. Pat. No. 4,073,354 and Rohde, et al. U.S. Pat. No. 4,098,363. An example of cutting inserts using polycrystalline diamond cutters and an illustration of a drill bit using such cutters, is found in Daniels, et al. U.S. Pat. No. 4,156,329.
The most comprehensive treatment of this subject in the literture is probably the chapter entitled STRATAPAX bits, pages 541-591 in ADVANCED DRILLING TECHNIQUES, by William C. Maurer, The Petroleum Publishing Company, 1421 South Sheridan Road, P. O. Box 1260, Tulsa, Okla. 74101, published in 1980. This reference illustrates and discusses in detail the development of the STRATAPAX diamond cutting elements by General Electric and gives several examples of commercial drill bits and prototypes using such cutting elements.
Polycrystalline diamond inserts have had extensive treatment in the literature as cutting elements for drill bits but there has been no suggestion of the use or application of diamond elements for friction bearings and particularly for bearings in turbodrills where the conditions of load and wear are severe.
Rotary seals are currently the weakest link in down-hole motor design. Improved seals, particularly in combination with improved bearing designs, would allow the bearings to be sealed in lubricant, thereby increasing their life substantially. Improved seals would allow bits to be operated at higher pressures thereby greatly increasing drilling rate.
There are six basic types of seals that have been tested in down-hole motors:
Existing drilling motors allow drilling mud to continuously leak through the rotary seals by constricting the flow with any of a variety of seals permitting leakage. Sand and other abrasive particles are filtered out of the mud in the rotary seals which results in rapid failure of the seals. Any substantial improvement in turbodrill design will require positive seals which allow no appreciable leakage.